The present invention relates to an articulated vertebral body spacer suitably inserted between vertebras such as cervical vertebras, thoracic vertebras, and lumbar vertebras, an intervertebral cavity measuring device, and a vertebral body spacer model.
In the case of a hernia of an intervertebral disk or a rupture of a vertebral body due to a malignant tumor, the intervertebral disk or the vertebral body is surgically removed. If the space left after the removal is narrow, no special treatment is performed. If the space is wide, a patient's own peripheral bone, an artificial vertebral body, or the like is inserted between the vertebras. If an autologous bone is used, it is free from a rejection symptom. An artificial vertebral body used nowadays is free from a rejection symptom and has a strong affinity for a bone.
The spine has a movable structure. If, therefore, a rigid intervertebral spacer is inserted between movable portions of the spine, the vertebral bodies and the spacer may be physically separated from each other every time the spine moves, even though the spacer has a strong affinity for a bone. For this reason, the present applicant has proposed articulated vertebral body spacer (Japanese Patent Application No. 2-217062). This spacer is constituted by a pair of upper and lower members respectively having concave and convex joint surfaces on their opposite surfaces. With this structure, a uniform pressure is applied to the contact surfaces between the vertebral bodies and the spacer so as to prevent separation or disengagement of the spacer.
The following problem, however, is posed in the articulated vertebral body spacer previously proposed by the present applicant, which spacer is constituted by the pair of upper and lower members respectively having concave and convex sliding contact surfaces on their opposite surfaces. Since the entire opposite surfaces of the upper and lower members are sliding contact surfaces, the spacer cannot restrict the inclination of the vertebral bodies. If, therefore, the vertebral bodies are inclined greatly, the joint may be separated or disengaged from the vertebral bodies. When a plurality of vertebral bodies are replaced, by increasing the number of joints to two or three, physiological curves can be formed in vertebral bodies. With these curves, it is expected that the disengagement of an artificial vertebral body join (articulated vertebral body spacer) can be prevented.
In a surgical operation on the cervical vertebras, an intervertebral disk is removed. Measurement of the depth and thickness of this intervertebral disk ablation cavity (intervertebral cavity) is indispensable for the insertion of a vertebral body spacer. A conventional depth gage for measuring the depth of an intervertebral cavity is a rod-like member and is insufficient for measurement of depth and thickness. If a vertebral body spacer model is formed, and an intervertebral cavity is formed to fit thereto, it is expected that insertion of an articulated vertebral body spacer can be easily and reliably performed.